Coated, flexible flat material

ABSTRACT

This invention relates to grained, textile flat materials coated with PU systems and to a process for the production thereof and to the use of such flat materials as a decorative starting material.

BACKGROUND OF THE INVENTION

[0001] This invention relates to grained, textile flat materials coated with polyurethane (PU) compositions and to a process for the production thereof and to decorative starting materials comprising such flat materials.

[0002] It has long been known to produce coated textile flat materials, for example for the production of artificial leather. The coating composition is applied onto the substrate in single or multiple layers in the direct coating process or using the transfer process. The coated textile flat materials may be used, for example, for the production of outer clothing, material for shoe uppers and linings, material for purses and similar articles, material for upholstery and for automotive interior trim.

[0003] The following processes are known to the person skilled in the art for the production of a grain or embossed pattern on coated textiles or other flat materials, all of which processes, however, are associated with disadvantages:

[0004] A predetermined pattern is embossed onto a coated support material by the action of heat and pressure on embossing calendars, embossing plates or also transfer papers. This embossing creates a grain which, however, gives rise to unwanted hardening as a result of the localized compaction. This relatively elaborate process is only performed using thermoplastic PU solutions, which sometimes still contain solvent residues which are vaporized by the action of heat.

[0005] Uncontrolled grain patterns may be achieved by treating materials which have been coated using two component PU solutions, if these materials are treated for a certain time using temperatures of for example 20 to 100° C. in an axial centrifugal dryer with an alternating direction of running (for example DE-A 1 760 260). Disadvantages of this process are not only the use of organic solvents, but also the necessity of precise timing of the process steps, which means that the grain must be formed before the system has actually crosslinked.

[0006] In the reversal process, embossed surfaces are produced by using grained release materials, in particular release papers or silicone molds. The embossed patterns produced with release papers are, however, relatively flat and must be predetermined as early as during the actual coating operation. Using silicone molds is highly cost-intensive and only acceptable for special effects.

[0007] An object of the present invention was to provide a process for the production of a deep grain profile on textile flat materials, which process does not exhibit the above-stated disadvantages, and thereby to obtain high quality products by a simple process.

[0008] It has surprisingly been found that coated flat materials comprising a grain are obtained if textile flat materials having residual shrinkage are first coated by the direct or reversal process with PU dispersions or solutions and are then subjected to heat treatment.

SUMMARY OF THE INVENTION

[0009] The invention relates to a process for the production of grained flat materials comprising coating a textile flat material, which has residual shrinkage, with a polyurethane (PU) dispersion or solution and then post-treating the textile flat material under the influence of heat.

[0010] The invention also relates to a grained, coated textile flat material obtained by using the process according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0011] Textile flat materials for the purposes of the present invention include, for example, woven and knitted fabrics, bonded and unbonded nonwovens and microfibre nonwovens. These may be made from synthetic, natural fibres and/or blends thereof. In principle, in addition to textiles, any other flexible flat materials are suitable for the process according to the invention, provided that they have residual shrinkage.

[0012] In textile materials consisting of fibre blends containing polyester fibres, residual shrinkage may be increased by splitting, as this reduces the content of polyester fibres and thus the harder fraction of the woven fabric.

[0013] It has proved advantageous in order to form a very deep grain profile to fill and stabilize the textile flat materials by means of PU coagulation before coating with polyurethane. Accordingly, this is a preferred embodiment of the present invention.

[0014] Reactive or post-crosslinking PU dispersions, as are for example described in WO 00/34352, are in particular suitable for pretreating the flat materials by coagulation. In this case, the PU dispersion, consisting of blocked isocyanate groups and at least one polyamine, is precipitated by thermal treatment to form a stable, partially crosslinked polyurethane or gel.

[0015] Coagulation is particularly suitable for producing films, for coating the most varied materials and for partially or completely impregnating nonwovens, knitted fabrics or other flat materials for the purpose of stabilization.

[0016] The reactive, post-crosslinkable PU dispersions are applied, for example, by flooding, spraying, dipping, spray application, slop-padding, with a doctor knife or roll or by padding, wherein the dispersions may be used in liquid or foamed form.

[0017] Once the coating has been applied, it is generally coagulated by dipping in water at a temperature of 50° C. to 120° C., preferably of 75° C. to 98° C. or with hot steam or in an oven by means of radiant heat or high frequency dryers. It is then usually dried at 60° C. to 180° C., preferably at 10° C. to 140° C. and condensation is performed at 140° C. to 165° C.

[0018] The flat materials are held in a stenter frame during crosslinking and drying in order to avoid premature shrinkage of the flat material.

[0019] The resultant coagulate is so resistant, that the precipitation operation after the application can be performed even in the saponification and splitting bath (3% NaOH). In the case of, for example, microfibre nonwovens containing polyester, the polyester content may simultaneously be saponified and dissolved out in that bath. This results in particularly soft flat materials with a pleasant handle.

[0020] The coated or filled flat materials may also subsequently be sanded and, in this case, are particularly soft. Mechanical treatment in a tumbling machine also increases softness.

[0021] It is also possible to precede the process according to the invention with other aqueous coagulation processes for stabilization, for example electrolyte or thermal coagulation of dispersions.

[0022] Electrolyte coagulation proceeds by immersing the coated substrate into a concentrated salt solution or into water combined with acid or the like, wherein the binder coagulates due to the elevated electrolyte content.

[0023] In thermal coagulation, non-post-crosslinkable binders with a heat-sensitive formulation are able to coagulate due to an increase in temperature.

[0024] The precleaned and optionally stabilized textile flat materials are then coated in known manner with the polyurethane systems by the direct or reversal process.

[0025] Coating compositions suitable for the process according to the invention are, for example, both single component and two-component polyurethane systems known in the textiles and leather industry which consist of isocyanate prepolymers and crosslinking agents. They are commercially available as solutions.

[0026] The aqueous single component polyurethane dispersions described in DE-A 4 236 569, which additionally contain hydrophilic structures, are suitable coating compositions for the process according to the invention.

[0027] Solvent-free, two-component polyurethane systems consisting of a blocked isocyanate prepolymer and polyamine, which are described for example in EP-A 0 784 097, are particularly suitable. These systems have good wet adhesion and excellent water-resistance. Mixtures of various PU systems are also suitable.

[0028] Coating compositions based on PU dispersions, described for example in DE-A 42 36 569, are suitable for the purpose of increasing the wearability of the coated flat materials, as the coatings produced with these PU dispersions are permeable to water vapour.

[0029] In the direct process, the PU coatings are applied onto the substrate by direct spreading using doctor knives, rolls or doctor wires.

[0030] As a rule, two or more, but preferably two, coats are applied in succession, such that the total thickness of the coating comprising base and topcoat layer(s) is 10 to 100 μm, preferably 20 to 60 μm. A paste which dries to yield a microporous layer, as described in DE-A 2 020 153, may also be used as the base coat. The subsequently applied topcoat protects the overall structure from mechanical stresses and abrasion.

[0031] The coating structure comprising base coat and topcoat may, however, also be applied by the so-called reversal process.

[0032] The reversal process is advantageous when highly flexible substrates, such as knitted fabrics, nonwovens or other non-continuous flat materials, are used.

[0033] In this case, the topcoat is initially applied by doctor knife onto a grained or also ungrained transfer paper and dried. A preferably foamed intermediate coat is then optionally applied. After application of a second base or adhesion coat, the substrate is gently pressed into the still wet layer. After drying, a solid composite comprising coating and substrate is obtained, which is removed from the release support and the structure of which largely corresponds to that of the above-described direct coating. After crosslinking, a coated and, depending upon the transfer paper, optionally superficially grained article is obtained.

[0034] Once dry, the coated flat material may be stored in this form and subsequently subjected to a post-treatment, during which the desired grain and colour may be imparted to the article.

[0035] A grain pattern may be achieved by simply pre-embossing the flat material coated according to the invention, as, under the action of heat in the post-treatment, a matching, but substantially deeper grain forms in the indentations arising from the pre-embossing. Without this pre-embossing, post-treatment yields a somewhat randomly grained product.

[0036] The flat materials coated by the direct process may optionally be subjected to a gentle pre-embossing by means of embossing or goffering calenders.

[0037] In the case of the reversal process, pre-embossing to form the grain may be produced by a grained transfer paper. When untextured release papers or simple dull-finish calendars are used, a random grain is obtained on post-treatment.

[0038] Post-treatment of the coated textile flat materials comprises a subsequent dyeing process or a tensionless treatment with boiling water. In the case of treatment with hot water, it is also possible to add suitable pigments directly to the coating compositions.

[0039] The coating and support material are coloured using acid dyes, disperse dyes or metal complex dyes depending upon the composition of the base material. Low-tension dyeing processes with a long liquor ratio, as is for example possible with reel vat dyeing, are particularly suitable. Metal complex dyes applied direct or also as a lacquer formulation yield the best wet fastness values of the PU coating.

[0040] Once the dyeing process is complete, neutralization is optionally performed and then thorough rinsing is carried out. Softeners to improve tactile properties may be applied through additives in the final rinsing baths, before the material is dried under low tension. When support materials containing cellulose are used, tumbling machine treatment to eliminate any possible wet rigidity is advisable.

[0041] The flat materials according to the invention may be used as a decorative starting material, for example as an outer clothing material, material for shoe uppers and linings, material for purses and similar articles, material for upholstery and for automotive interior trim.

EXAMPLES

[0042] I. Pretreatment of Cleaned Textile Flat Material:

Example 1 (According to the Invention)

[0043] Stabilization by aqueous coagulation with a reactive dispersion. Formulation: 90-180 parts by weight of Impranil ® VP LS 2333 (butanoeoxime blocked MDI prepolymer) (Bayer AG, Leverkusen) 1-2.7 parts by weight of Imprafix ® VP LS 2330/ isopropanol (1:1) (diamine cross- linking agent) (Bayer AG, Leverkusen) 910-820 parts by weight of deionized water.

[0044] The solids content of the dispersion formulation was 4 to 8%.

[0045] The textile flat article was padded with the dispersion formulation (100% liquor absorption) and then coagulated in a steamer at 98° C.

[0046] Complete crosslinking and drying was performed on a stenter frame at 165° C.

[0047] Sometimes the nonwoven, for example, polyester and polyamide fiber blends, used were treated with splitting during or after completion of coagulation in order to achieve a softer product handle. To this end, the nonwoven was treated, for example, for approx. 1 hour in 3% sodium hydroxide solution at boiling point, wherein the polyester content was dissolved out.

[0048] Prior sanding of the substrate surface enhanced the effect.

Example 2 (According to the Invention)

[0049] Stabilization by coagulation with a conventional dispersion. Formulation: 200 parts by weight of Impranil ® DLV dispersion (aqueous polyurethane dispersion) (Bayer AG, Leverkusen) 4 parts by weight of Koagulant ® WS (20%) (Bayer AG, Leverkusen) 16 parts by weight of aqueous sodium chloride solution (10%) 4 parts by weight of Euderm ® Driver DE (Bayer AG, Leverkusen) 2 parts by weight of Bayderm ® Fix CIN (Bayer AG, Leverkusen) 774 parts by weight of water.

[0050] The textile was padded with the dispersion formulation (100% liquor absorption) and then dried on a stenter frame.

[0051] Splitting of a polyester/polyamide nonwoven could be performed in a similar manner to Example 1.

Example 3 (According to the Invention)

[0052] When coagulation to stabilize the textile flat material was not performed, the cleaned, scalded textile was dried on a stenter frame. Topcoat: 650 parts by weight of Impranil ® DLN dispersion (aqueous polyester-polyurethane dispersion) (Bayer AG, Leverkusen) 350 parts by weight of Impranil ® DLF dispersion (Bayer AG, Leverkusen) thickened with Mirox ® AM (Stockhausen, Krefeld) in the presence of ammonia. Intermediate coat: 500 parts by weight of Impranil ® DLN dispersion (polyurethane mixture) (Bayer AG, Leverkusen) 500 parts by weight of Impranil ® VP LS 2333 (Bayer AG, Leverkusen) 7.5 parts by weight of Imprafix ® VP LS (Bayer AG, Leverkusen)/isopropanol (1:1) 20 parts by weight of Stockal ® STA (Stockhausen, Krefeld) 30 parts by weight of Stockal ® SR (Stockhausen, Krefeld) are mechanically foamed to 500 g/L and thick- ened with Mirox ® AM (Stockhausen, Krefeld) in the presence of ammonia. Adhesion coat: 1000 parts by weight of Impranil ® VP LS 2333 (Bayer AG, Leverkusen) 15 parts by weight of Imprafix ® VP LS 2330 (Bayer AG, Leverkusen)/isopropanol (1:1) are thickened with Mirox ® AM (Stockhausen, Krefeld) in the presence of ammonia.

[0053] Coating was performed by both the direct and reversal process.

[0054] When reversal coating was performed using an embossed transfer paper, the grain of the coating was sometimes structurally predetermined and deepened or enhanced by the post-treatment.

[0055] When a smooth transfer paper was selected, the grain obtained by post-treatment was random, as it was also in the case of direct coating.

[0056] III. Post-Treatment of the Coated Textile Flat Material

[0057] In case the coated textile was post-treated only with hot water, suitable pigments were added directly to the coating paste.

[0058] Polyurethane was generally dyed with metal complex dyes (for example complexing azo dyes, porphyrins or phthalocyanines) and selected acid and disperse dyes (for example azo, triarylmethane or anthraquinone dyes). In the case of tone-in-tone dyeing with the substrate, depending upon the dyeing process and substrate, these dyes were also be combined with other classes of dye.

[0059] The following details constitute one option for simple dyeing, for example on the reel:

Example (According to the Invention)

[0060] Dyes used: Telon ® monosulfonic acid dye dyes (Dystar, Leverkusen) Isolan S ® 1:2 metal complex dyes dyes (Dystar, Leverkusen) Liquor ratio: 1:40 deionized water Dye 2 to 4% of fabric weight concen- tration: Temperature 40° C.

30 min

100° C.

60 min

100° C. profile during dyeing:

[0061] When dyeing was performed with acid dyes, the pH value was adjusted to 5 with acetic acid.

[0062] Neutralisation was then performed with sodium hydroxide solution, the fabric was rinsed with deionized water and then dried without tension, for example on a festoon dryer.

[0063] Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims. 

1. A process for the production of grained flat materials comprising coating a textile flat material, which has residual shrinkage, with a polyurethane (PU) dispersion or solution and then post-treating the textile flat material under the influence of heat.
 2. The process of claim 1 wherein the textile flat material is coating step comprises the direct process or the reversal process.
 3. The process of claim 1 further comprising, prior to PU coating, stabilizing the textile flat material by aqueous coagulation with a reactive and post-crosslinkable PU dispersion.
 4. The process of claim 1 further comprising, after PU coating, pre-embossing the textile flat material.
 5. The process of claim 1 wherein post-treating comprises dyeing or treating the flat material tensionless with hot water.
 6. A grained, coated flat material obtained by the process of claim
 1. 7. A decorative starting material containing a grained, coated flat material obtained by the process of claim
 1. 8. The decorative starting material of claim 7, wherein the material is selected from the group of outer clothing material, material for shoe uppers, material for shoe linings, material for purses and similar articles, material for upholstery and material for automotive interior trim. 